This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-075962, filed Mar. 16, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an X-ray diagnostic apparatus capable of changing an angle of radiography.
2. Description of the Related Art
In an X-ray diagnostic apparatus, an X-ray grid for eliminating a scattered ray is usually arranged in an image reception plane of an image intensifier or a flat panel type X-ray detector. The X-ray grid is constituted by assembling many laminated plates of metal or the like in the form of a grid or in parallel. In the prior art, since a gap between the grid plates (which will be referred to as grid density hereinafter) is relatively smaller than the solution of a radiographic system, the moire does not appear in an image as an artifact.
However, with recent increase in the resolution of the radiographic system, the grid appears in an image as the moire-like artifact.
Of course, the moire can be seemingly dissolved in principle by narrowing the grid density so that the radiographic system can not recognize it. However, the grid density is configured by the order of several tens per 1 cm even now, and the X-ray grid can not be constituted with the narrower density. Even if the X-ray grid can be constituted with the narrower density, the manufacturing cost becomes too high. Therefore, solving this problem by processing the grid is not realistic.
Further, for example, Jpn. Pat. Appln. KOKAI Publication No. 11-146277 discloses elimination of the moire by image processing. That is, when an image of a uniform phantom is taken in place of a patient, moire image data is basically obtained, and elimination of the moire can be realized by actually subtracting the moire image data from patient image data.
This moire elimination method, however, can not be applied to X-ray diagnosis of the circulatory system or the like in some cases. The paramount reason is that the pattern of moire fringes varies in many ways depending on a radiographic angle or an SID (Source Image Distance), for example.
It is an object of the present invention is to improve the moire correction accuracy in an X-ray diagnostic apparatus.
According to a first aspect of the present invention, there is provided an X-ray diagnostic apparatus comprising: an X-ray tube; an X-ray detector; a grid arranged on an image reception plane of the X-ray detector; an arm which supports the X-ray tube and the X-ray detector in such a manner that a distance between the X-ray tube and the image reception plane of the X-ray detector can be changed; an arm support device which supports the arm in such a manner that an angle of the arm can be changed; a storage device which stores files of moire image data obtained by the grid in association with at least one of the distance and the angle; and a moire correction circuit which corrects image data outputted from the X-ray detector based on moire image data selectively read from the storage device in accordance with at least one of the distance and the angle from the storage device.
According to a second aspect of the present invention, there is provided an X-ray diagnostic apparatus comprising: an X-ray tube; an X-ray detector; a grid arranged on an image reception plane of the X-ray detector; an arm which supports the X-ray tube and the X-ray detector in such a manner that a distance between the X-ray tube and the image reception plane can be changed; an arm support device which supports the arm in such a manner that an angle of the arm can be changed; a moire correction data generation circuit which performs frequency analysis of image data outputted from the X-ray detector, specifies a spatial frequency corresponding to a moire pattern and generates moire correction data based on the specified spatial frequency; and a moire correction circuit which corrects image data outputted from the X-ray detector based on the generated moire correction data.
According to a third aspect of the present invention, there is provided an X-ray diagnostic apparatus comprising: an X-ray tube; an X-ray detector; a grid arranged on an image reception plane of the X-ray detector; an arm which supports the X-ray tube and the X-ray detector in such a manner that a distance between the X-ray tube and the image reception plane of the X-ray detector can be changed; an arm support device which supports the arm in such a manner that an angle of the arm can be changed; a frequency analysis circuit which is configured to perform frequency analysis of image data outputted from the X-ray detector and specify a spatial frequency corresponding to a moire pattern; and a moire correction circuit which is configured to attenuate specified spatial frequency component of the image data outputted from the X-ray detector.
According to a fourth aspect of the present invention, there is provided an X-ray diagnostic apparatus comprising: an X-ray tube; an X-ray detector; a grid arranged on an image reception plane of the X-ray detector; an arm which supports the X-ray tube and the X-ray detector in such a manner that a distance between the X-ray tube and the image reception plane of the X-ray detector can be changed; a sensor which detects a distance between the X-ray tube and the image reception plane of the X-ray detector; an arm support device which supports the arm in such a manner that an angle of the arm can be changed; a storage device which stores moire image data when the distance between the X-ray tube and the image reception plane of the X-ray detector is a reference distance; a moire image enlargement circuit which is configured to enlarge the moire image data based on the distance detected by the sensor and the reference distance; and a moire correction circuit which corrects the image data outputted from the X-ray detector based on the enlarged moire image data.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.